In an analog television, a composite video signal of an image comprises a luminance signal (Y) and a chrominance signal (C). A comb filter is commonly used to separate the luminance signal and the chrominance signal from the composite video signal. The process of separating the luminance signal and the chrominance signal is referred to as a Y/C separation.
There are three types of comb filters used to separate the composite video signal. The three types of comb filters are classified into a one-dimensional (1D) comb filter, a two-dimensional (2D) comb filter and a three-dimensional (3D) comb filter. The 1D comb filter and the 2D comb filter are referred to as a type of non-3D comb filter. In general, the non-3D comb filter is used to separate the luminance signal and the chrominance signal when an image is under a motion condition, and the 3D comb filter is used to separate the luminance signal and the chrominance signal when the image is under a static condition.
When the image which is under the static condition is affected by noises, the image appears to be under a slow motion condition. As a result, using the non-3D comb filter may cause an unstable and sparkle-like situation. That is, the image is not really motional, but the non-3D comb filter is wrongly used. Therefore, there is a need for a solution to compensate a luminance signal which is outputted by the non-3D comb filter for avoiding the unstable and sparkle-like situation.